At the very end of a previous CP retrofit delivery for the Southern Norwegian shelf, FORCE Technology Norway has been awarded another retrofit project from an operator in the Northern North sea for a large, ageing jacket structure.

This project was a bit more challenging than the previous, as depolarization of the structure was well in process and seawater depth was around 100 meters; this meant that current requirements were quite high to re-polarise the jacket back to protection criterion. Furthermore, many surrounding structures at the seabed led to several exclusion zones challenging positioning of the anode pods.

However, using our SeaCorr™ CP computer modelling software and thorough assessment of a range of CP inspection data, the retrofit design and solution was optimised in terms of extent of subsea intervention with positioning of the anode pods also including adequate tie-back cable dimensioning and other technical means for retrofit. To overcome the quite high retrofit current demand, we could still use our standard anode pods; we merely used Magnesium anodes with necessary mitigation to prevent over polarisation of the sleds risking hydrogen embrittlement and coating disbonding during service life.

CP retrofit of offshore jacket
CP model of the jacket calibrated with inspection data prior to retrofit.
CP retrofit of offshore jacket structure in the North sea
CP model with calculated potential distribution after retrofitting 12 anode pods
with Magnesium anodes.